1. Field of the Invention
The present invention relates in general to the biotechnology field and, in particular, to a multiwell plate made from a plastic upper plate and a transparent bottom plate that are joined to one another.
2. Description of Related Art
The recent growth in many areas of biotechnology has increased the demand to perform a variety of studies, commonly referred to as assays, of biochemical systems. These assays include for example, biochemical reaction kinetics, DNA melting point determinations, DNA spectral shifts, DNA and protein concentration measurements, excitation/emission of fluorescent probes, enzyme activities, enzyme co-factor assays, homogeneous assays, drug metabolite assays, drug concentration assays, dispensing confirmation, volume confirmation, solvent concentration, and solvation concentration. Also, there are a number of assays which use intact living cells that require visual examination.
Assays of biochemical systems are carried out on a large scale in both industry and academia, so it is desirable to have an apparatus that allows these assays to be performed in a convenient and inexpensive fashion. Because they are relatively easy to handle, are low in cost, and generally disposable after a single use, multiwell plates are often used for such studies. Multiwell plates are typically formed from a polymeric material and consist of an ordered array of individual wells. Each well includes sidewalls and a bottom so that an aliquot of sample can be placed within each well. The wells may be arranged in a matrix of mutually perpendicular rows and columns. Common sizes for multiwell plates include matrices having dimensions of 8×12 (96 wells), 16×24 (384 wells), and 32×48 (1536 wells).
The materials used to construct a multiwell plate are selected based on the samples to be assayed and the analytical techniques to be used. For example, the materials of which the multiwell plate is made should be chemically inert to the components of the sample or any biological or chemical coating that has been applied to the multiwell plate. Further, the materials should be impervious to radiation or heating conditions to which the multiwell plate is exposed during the course of an experiment and should possess a sufficient rigidity for the application at hand.
In many applications, a transparent window in the bottom of each well is needed. Transparent bottoms are primarily used in assay techniques that rely on emission of light from a sample within the well and subsequent spectroscopic measurements. Examples of such techniques include liquid scintillation counting and techniques which measure light emitted by luminescent labels, such as bioluminescent or chemiluminescent labels, fluorescent labels, or absorbance labels. Optically transparent bottom wells also enable microscopic viewing of specimens and living cells within the well. Currently, optically transparent and ultraviolet transparent bottomed multiwell plates exist in the market and are used for the aforementioned purposes. These multiwell plates are typically made from a hybrid of different polymeric materials, one material making up the sidewalls of the wells and another material making up the bottom walls of the wells.
Preferably, multiwell plates that are used for spectroscopic and microscopic measurements would have well bottoms made from glass. Glass has the advantage of being chemically inert, has superior optical properties in the visible range, is rigid, and is highly resistant to any deformation process caused by heating, due to its high melting temperature. Further and unlike most polymers, glass can be formulated and processed to provide a surface which produces very little background signal (barring absorbance) and which may be manufactured to extreme smoothness. While it is simple to make glass in sheets, it is not possible to injection mold articles made from glass, and it is extremely difficult to press a molten gob of glass into an industry standard multiwell plate format. A solution to the problem is to join a plastic upper plate that forms the sidewalls of the wells of a microplate to a substantially flat transparent glass lower plate that forms the bottom walls of the wells. One commonly employed method of joining a plastic upper plate and a glass lower plate to one another is to use an adhesive. Unfortunately, the multiwell plate that uses an adhesive to bond together the plastic upper plate and glass lower plate does not perform well under normal cell culture conditions. In particular, adhesive migration into the test wells is particularly troublesome as the presence of adhesive in the work area of the optical bottom surface of the well may potentially alter the assay results. Additionally, the presence of adhesive in the interior of the wells may interfere with the creation and reading of microassays, cell adhesion and growth, and binding and assaying of nucleic acids, proteins, and other biological or chemical agents. Adhesives which are UV cured or UV stabilized also have the tendency to absorb UV light, which may result in altering fluorescent readings taken from a detector located above or below the respective well. Accordingly, there is a need for a multiwell plate that has a strong adhesive bond between the plastic upper plate and the glass lower plate, but does not encounter the problem of adhesive migration into the test well. This need and other needs are satisfied by the multiwell plate and the method of the present invention.